Abstract 1448: Serine 21 Phosphorylation of GSK-3α Mediates Myocyte Proliferation through CyclinD1/E2F Pathway under Pressure Overload
Serine(S)21/S9 phosphorylation of glycogen synthase kinase-3α (GSK-3α) and GSK-3β, respectively, by upstream kinases, such as Akt, inhibits GSK-3. In order to elucidate the role of S21/S9 phosphorylation in regulating growth and death of cardiac myocytes, we analyzed homozygous GSK-3α and β knockin mice (αKI and βKI), in which S21 or S9 was replaced with alanine. Unexpectedly, inhibition of S21 and S9 phosphorylation exhibited opposite impacts on the heart under pressure overload (PO): inhibition of S9 phosphorylation in GSK-3β attenuated PO-induced cardiac hypertrophy, apoptosis, fibrosis, and heart failure (HF). Conversely, inhibition of S21 phosphorylation in GSK-3α promoted hypertrophy, apoptosis, fibrosis, and HF. DNA microarray and pathway analyses showed that genes involved in cell proliferation were stimulated in βKI and wild type (WT) but not in αKI after transverse aortic constriction (TAC). The number of Ki67 (+) myocytes after TAC was significantly smaller in αKI than in βKI or WT (0.09, 0.26, 0.30 per field, #p<0.05 vs WT). The total number of myocytes in the heart after TAC was significantly smaller in αKI than in βKI or WT. Transcription factor binding site analysis, using the result of microarray, indicated that E2F, a key regulator of cell proliferation, was stimulated after TAC in βKI or WT but not in αKI. In order to examine whether suppression of cell cycle regulators is involved in the development of HF after TAC in αKI mice, adenovirus vectors harboring cyclinD1 with nuclear localization signal (Ad-cycD1) or LacZ (Ad-LacZ) were injected into αKI hearts 2 days before TAC. After 2 weeks, LVEF was greater (66±4 vs 53±3%, p<0.05, n=7, 8) and lung weight/ tibial length (TL) (p<0.05) was smaller in Ad-cycD1 injected hearts than in Ad-LacZ hearts. HW/TL (9.7±0.4 vs 13.4±0.7, p<0.05, n=5, 7) was significantly smaller in Ad-cycD1 than in Ad-LacZ hearts. The extent of LV fibrosis and the number of TUNEL (+) cells were significantly smaller in Ad-cycD1 than in Ad-LacZ hearts. These results suggest that overexpression of cyclinD1 rescued cardiac dysfunction in αKI after TAC. Collectively, stimulation of GSK-3α, but not GSK-3β, negatively regulates the cell cycle machinery, such as the cycD1-E2F pathway, thereby causing cardiac dysfunction under PO.
This research has received full or partial funding support from the American Heart Association, AHA National Center.